feat(doctor): add fn doctor CLI + 14 functions for system management

Adds `fn doctor` read-only diagnostic command with subcommands artefacts,
services, sync, uses-functions, unused, and --json flag for agents.
Each subcommand wraps a registry function in functions/infra/.

New functions:
- artefact_doctor, services_status, pc_locations_drift,
  audit_uses_functions, find_unused_functions (Go diagnostics)
- backup_sqlite_db, rotate_backups, wait_for_http, wait_for_port,
  port_kill, tail_journal, pre_commit_hook_install (bash utilities)
- notify_telegram (Go HTTP)
- backup_all pipeline (tag launcher)

Plus prior session leftovers (scan_secrets_in_dirty, append_diary_entry,
git utilities, http_session_cookie_middleware, compile/full-git pipelines).

Fixes pc_locations_drift filepath.Join bug with absolute dir_path.
Documents fn doctor in CLAUDE.md, .claude/rules/fn_doctor.md (rule 23),
docs/architecture.md, CHANGELOG.md (2026-05-07), and diary entry.

First fn doctor uses-functions run found drift in 7/12 apps (deuda
para sincronizar app.md con imports reales).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

cmd/fn/main.go

@@ -45,6 +45,8 @@ func main() {
 		cmdAnalysis(os.Args[2:])
 	case "sync":
 		cmdSync(os.Args[2:])
+	case "doctor":
+		cmdDoctor(os.Args[2:])
 	case "help", "-h", "--help":
 		printUsage()
 	default:
@@ -70,7 +72,9 @@ Usage:
   fn project <init|list|show|status>       Gestiona proyectos
   fn app     <list|clone|pull>             Gestiona apps externas (Gitea)
   fn analysis <list|clone|pull>            Gestiona analyses externas (Gitea)
-  fn sync    [status|locations]            Sincroniza con servidor central`)
+  fn sync    [status|locations]            Sincroniza con servidor central
+  fn doctor  [artefacts|services|sync|uses-functions|unused] [--json]
+                                           Diagnostico read-only del registry`)
 }
 
 func root() string {